1. Field of the Invention
The present invention relates generally to semiconductor devices and, more particularly, to the fabrication of a buried digit line in a memory device.
2. Description of the Related Art
This section is intended to introduce the reader to various aspects of art which may be related to various aspects of the present invention which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Microprocessor-controlled integrated circuits are used in a wide variety of applications. Such applications include personal computers, telephones, portable devices, networks, and a host of other consumer products. As is well known, microprocessors are essentially generic devices that perform specific functions under the control of a software program. This software program is stored in a memory device that is coupled to the microprocessor. Not only does the microprocessor access the memory devices to retrieve the software program instruction, but it also facilitates storage and retrieval of data created during the execution of the program in one or more of the memory devices.
It should be understood that the memory devices are typically mass produced through fabrication processes to form various structures in a semiconductor chip. In forming the structures, different materials are layered together to form signal paths or circuitry that are utilized by the memory device. These structures are connected together to facilitate the exchange signals and distribute power throughout the semiconductor chip. Additionally, the structures within the semiconductor chip may be divided into different sections, such as an array section and a peripheral section. The array section may include memory structures, such as memory cells and banks that are used to store data, while the peripheral section may include larger structures that support the array, such as drivers, decoders and/or other similar circuitry.
Regardless of the specific structures being fabricated, it is often desirable to minimize the size of the structures to allow for greater density and to reduce the contact resistance between different structures within the semiconductor chip. Generally, the critical dimensions of the structures patterned on the semiconductor chips are becoming increasingly complex as the structures are designed to operate at higher speeds. As these critical dimensions change, the electrical properties of the structures and integrated circuits vary in relation to the critical dimensions. Therefore, it is important to maintain the critical dimensions to achieve consistency in the electrical properties of the structures.
For instance, in stack capacitor dynamic random access memory (DRAM) cells, cell height may continue to increase, while the contact size is minimized. As a result, the contact resistance in the peripheral circuitry may increase, which makes high-speed designs for structures increasingly challenging. To reduce the contact resistances for the connections between the array section and the peripheral section of a memory device, a buried digit line (BDL) layer may also be utilized as a local interconnect (LI), which is a short interconnect between structures, or as a bus, which is a longer interconnect between structures. The buried digit line or local interconnect (BDL/LI) layer may have connections to different structures, such as dynamic random access memory (DRAM) cells, p-type metal oxide semiconductor (PMOS) gates, n-type metal oxide semiconductor (NMOS) gates, P+ active areas and N+ active areas, which are formed in the peripheral and array sections of the semiconductor chip.
In fabricating the BDL/LI layer, two to three masking layers are generally utilized in the fabrication process to provide access from the BDL/LI layer to different areas of the device. These additional masking layers consume valuable fabrication time and increase the cost of manufacturing the semiconductor chip. Accordingly, minimizing the masking layers and corresponding deposition/etch steps may enhance the fabrication process of the semiconductor chip.